Logging from the user code

Component: NServiceBus
NuGet Package: NServiceBus (7.2 - 7.3)

Logging is done via the Microsoft.Extensions.Logging abstraction either by hositing using the NServiceBus extension for the Microsoft Generic Host, or by using the NServiceBus extensions for Microsoft logging when self-hosting.

Using the NServiceBus logging abstraction

In legacy endpoints the NServiceBus logging abstraction is used for writing log messages from user code.

Set up a single static field to an ILog in the classes, and then use it in all methods:

public class ClassUsingLogging
{
    static ILog log = LogManager.GetLogger<ClassUsingLogging>();
    readonly int times = 2;

    public void SomeMethod()
    {
        log.Warn("Something unexpected happened.");
        if (log.IsDebugEnabled)
        {
            log.Debug("Something expected happened.");
            log.DebugFormat("Also, this other thing happened {0} times.", times);
        }
    }
}
Make sure that logging is correctly initialized before resolving the ILog instance. Not doing so can result in a logger using an incorrect configuration
To avoid unnecessary processing, especially when logging more verbose messages, such as Debug, make sure to first check if logging at that level is enabled.
Since LogManager.GetLogger(..); is an expensive call, it is important that the field is static so that the call happens only once per class and has the best possible performance.
The *Format APIs pass their message and format arguments to the corresponding APIs of the underlying logging framework so their behavior varies. Some frameworks, like NLog, use special syntax to create structured log entries. Refer to the documentation of the specific logging framework for details. The built-in logging uses string.Format to generate the message that is written.

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